In a conventional apparatus, for example, a switching device for a swirl control valve, a switching member is provided in a fluid passage (e.g. an intake passage, an exhaust passage, and so on), in which a fluid pressure pulsation is generated, and the switching member is operated by an electric motor through a speed reduction gear.
In the above apparatus, however, an electrical power is necessary for maintaining an opening degree of the switching member, even in the case that the switching member is continuously held at its certain switching position (e.g. at a fully-opened or a fully-closed position). This is because the opening degree of the switching member is held by the electric motor, to which the electrical power is supplied.
It is, therefore, proposed in the art to stop the supply of the electrical power to the electric motor when the switching member is continuously held at its certain switching position, by using a two-way clutch, which, on one hand, transmits a rotational force applied to a rotational driving unit to a rotational driven unit, and on the other hand, transmits a rotational force applied to the rotational driven unit not to the rotational driving unit but to a collar, which is a fixed member. Such a prior art is disclosed in, for example, PCT Patent Publication No. 00/08349, PCT Patent Publication No. 00/08350, or Japanese Patent Publication No. 2001-214946.
According to PCT Patent Publication No. 00/08349, or PCT Patent Publication No. 00/08350, a collar is arranged at an outer periphery of a rotational driven unit. According to Japanese Patent Publication No. 2001-214946, a collar is arranged at an inner periphery of a rotational driven unit.
A conventional two-way clutch will be explained with reference to FIG. 6.
The conventional two-way clutch has a rotational driving unit J1 rotated by an electric motor (not shown), and a rotational driven unit J2 to be rotated when it is brought into contact with the rotational driving unit J1 in a circumferential (rotational) direction. A non-rotatable member (an annular collar) J3 is provided at an outer periphery of the rotational driving unit J1. A roller J4 is disposed in a space between the rotational driven unit J2 and the collar J4.
An outer peripheral surface of the rotational driven unit J2 is opposed to an inner peripheral surface of the collar J3, such that a distance L1 of a large space portion between the rotational driven unit J2 and the collar J3 at a middle point of the outer peripheral surface is larger than a distance L2 of a small space portion between the rotational driven unit J2 and the collar J3 at a side point of the outer peripheral surface.
An outer diameter (a dimension in a radial direction) L3 of the roller J4 is so made to be larger than the distance L2 but smaller than the distance L1.
A projection J5 is formed at a circumferential side end of the rotational driving unit J1, such that the projection J5 pushes the roller J4 toward the large space portion (L1) when the rotational driving unit J1 is brought into contact with the rotational driven unit J2.
The above two-way clutch operates as below.
(In Motor Operation)
In the case that the electric motor is rotated in its forward or reverse direction, the rotational driving unit J1 is rotated by the rotational force applied to the rotational driving unit J1, so that the projection J5 pushes the roller J4 to the large space portion L1. As a result, the rotational driving unit J1 as well as the rotational driven unit J2 is brought into a condition, in which the units J1 and J2 are freely rotatable with respect to the collar J3. Then, the rotational driving unit J1 is brought into contact with the rotational driven unit J2, so that the rotational force of the rotational driving unit J1 is transmitted to the rotational driven unit J2 and the rotational driven unit J2 is rotated together with the rotational driving unit J1.
(When Power Supply to the Motor is Cut Off)
When the rotational force is applied to the rotational driven unit J2 during a condition, in which electrical power supply to the electric motor is cut off, the roller J4 is firmly held between the rotational driven unit J2 and the collar J3 as a result of even a small rotation of the rotational driven unit J2 with respect to the collar J3, so that the rotational driven unit J2 is engaged with the collar J3 by means of the roller J4, as shown in FIG. 6. Accordingly, the rotation of the rotational driven unit J2 is restricted.
The two-way clutches disclosed in the above mentioned patent publications are generally used for a vehicle power window system. If, however, the above clutch was applied to a switching device for the passage (e.g. the intake passage, the exhaust passage, or the like), in which the fluid pressure pulsation is generated, the clutch of the above kind may not sufficiently restrict the rotation of the switching device, when high vibration, high load, and/or large pulsation is applied to the switching device.
Accordingly, a performance for maintaining the switching device at its certain switching position is decreased.
In the case that the switching position is operated by a feed-back control, a number of operations for correcting the switching position will be extremely increased, and durability of a speed reduction gear, bearings, the electric motor and so on may be deteriorated.
The problem of the two-way clutch is explained as above, when it is applied to a driving mechanism of the switching device for the passage, in which the fluid pressure pulsation is generated. However, the same or similar problem may occur when the above two-way clutch is applied to any other purpose. Namely, the rotational driven unit may be moved (can not be held at a desired position) due to the high vibration, the high load, and/or the large pulsation, when the power supply to the electric motor is cut off.